The beneficial effect of Enterococcus faecium on the in vitro ruminal fermentation rate and extent of three typical total mixed rations in northern China

in vitro batch cultures were performed to determine the effect of Enterococcus faecium at inclusion levels of 0 (Control), 1.33, 2.67, 4, 5.33 and 6.67×106CFU/mL in culture fluids consisted of 25mL filtrated rumen fluid and 50mL buffer solution on rumen degradability, kinetics of gas production, and fermentation characteristics of 3 typical total mixed rations in northern China with different forage and/or concentrate ingredients (MF, a ration with a mixed forage combination of corn silage and alfalfa hay; CSA, a ration with a single forage of corn stalks and same concentrate in MF; CSB, a ration with same forage in CSA but concentrate ingredients different from MF and CSB). After 72h incubation, in vitro dry matter disappearance and cumulative gas production were greater in MF than CSA and CSB (P<0.001), and the fermentation characteristics varied depending on the ration incubated. Regardless of what type of ration was incubated, the in vitro dry matter disappearance, cumulative gas production, asymptotic gas production, and maximum gas production rate values were all greater in the E. faecium addition group than the control (P<0.010) and increased linearly with the augmentation of the E. faecium addition level (P<0.001). In comparison with the control, E. faecium addition slightly decreased pH, but did not alter ammonia N concentration. Microbial crude protein and total volatile fatty acid concentrations in the culture fluids were increased by the E. faecium addition (P<0.001), and molar acetate and butyrate proportions were decreased (P<0.001), but molar propionate and valerate proportions were increased (P<0.001). Methane production estimated by volatile fatty acids was decreased by E. faecium addition and fermentation efficiency was greater in the E. faecium addition in comparison with the control (P<0.001). In summary, rumen fermentation characteristics differed depending on forage ingredient and nutrient density in the rations; the E. faecium addition increased the in vitro rumen dry matter degradability and sped up the fermentation process, resulting in a remarkable increase in total VFA production (from 14.0 to 25.7%). E. faecium addition level of at least 2.67×106CFU/mL exhibited high potential for stimulating the growth of rumen microbes to increase the glucogenic propionate energy supply for host ruminants.